S. Reddy et al., DETERMINATION OF THE MAGNETIC-SUSCEPTIBILITY OF LABELED PARTICLES BY VIDEO IMAGING, Chemical Engineering Science, 51(6), 1996, pp. 947-956
Magnetic cell sorting is gaining in popularity as a method to separate
and recover viable cells which differ in functionality, but not in ph
ysical characteristics. We are developing a continuous cell sorter to
overcome the restrictions of current batch methods, which are limited
in their throughput and separation efficiency and which can also subje
ct cells to potentially detrimental physical stresses. Of primary impo
rtance in the design and operation of a continuous magnetic cell sorte
r is the degree of cell magnetization, which is characterized by a pro
perty called the magnetic susceptibility. Current techniques for measu
ring susceptibility give only population average values. We describe h
ere a video-based technique for quickly measuring the susceptibility o
f large numbers of individual particles. Paramagnetic particles are pu
mped across the interpolar gap of a permanent magnet and the magnetic
held-induced deflections are recorded by video microscopy. Susceptibil
ity is computed from force balances and the measured velocities for in
dividual particles. Our results show that this method can provide susc
eptibility values which agree well with values obtained from other est
ablished methods, while additionally providing population statistics n
ot available by the other methods. The versatility of this method is a
lso demonstrated.